1. Field of the Invention
The present invention relates to a cylinder device used for inserting or removing a core during die casting and plastic injection molding. More specifically, the invention relates to a cylinder device used when the core for forming a screw hole in a product is inserted or removed.
2. Description of the Related Art
Traditionally, in order to obtain a diecast product with a hole formed therein, a core pin is attached to a die by insertion, and when molten metal poured into a cavity formed by mold clamping has been solidified, the core pin is withdrawn, thereby forming the hole.
In this case, the molten metal is solidified after having been cooled and contracted. Consequently, when the core pin is withdrawn, galling or seizure between the core pin and the product tends to occur.
It has therefore become a common practice to provide a draft angle on the core pin in advance, thereby facilitating detachment of the core pin from the solidified molten metal. Generation of a defective product is thereby prevented.
Japanese Utility Model Unexamined Publication SHO61-167255 discloses a device that withdraws a core pin while rotating the core pin in order to reduce a force for withdrawing the core pin. Further, the applicant of the present invention proposes in Japanese Patent Unexamined Publication H10-131913 and Japanese Patent Unexamined Publication H11-62907 cylinder devices having a function of causing the core pin to perform the operation as described above.
A cylinder device disclosed in Japanese Patent Unexamined Publication H10-131913 has a configuration shown in FIG. 7.
This cylinder device has a basic structure of a single cylinder rod. A screw rod 55 is installed upright and fixed at a position on an inner wall surface of a head cover 51 on a side of a cylinder chamber 52, which faces an axial center 54 of a piston and rod 53. A male screw having a large lead angle is formed in an outer peripheral surface of the screw rod 55. The screw rod 55 has a stroke length longer than that of the piston rod 53.
On the other hand, a screwing board 57 is fixed to a rear end surface of a piston 56 of the piston and rod 53. In the screwing plate 57, a screw hole to be screwed together with the screw rod 55 is formed.
An axial hole 58 is formed in the piston and rod 53. The axial hole 58 extends from the rear end surface of the piston 56 along the axis center. The axial hole 58 has an inner diameter larger than a thread diameter of the screw rod 55, and deeper than a length obtained by subtracting the thickness of the screwing board 57 from the length of the screw rod 55.
When a port 61 that leads to a cylinder chamber 60 on a side of a rod cover 59 is connected to a drain and pressure oil is supplied through a port 62 that leads to the cylinder chamber 52 on a side of the head cover 51 in this configuration, the piston and rod 53 advances while rotating, due to a screwing relationship between the screw rod 55 and the screwing board 57. Conversely, when the port 62 is connected to the drain and the pressure oil is supplied through the port 61, the piston and rod 53 retracts while rotating in a direction opposite to the direction in which the piston and rod 53 advances.
Next, a cylinder device disclosed in Japanese Patent Unexamined Publication HEI11-62907 has a configuration shown in FIG. 8.
In this cylinder device, a pivotally supporting mechanism 73 which pivotally and rotatably supports one end of a rotary rod 72 while restraining movement of the rotary rod 72 in an axial direction is provided at a head cover 71 of a cylinder main body 70 of a two-port type.
The one end of the rotary rod 72 is pivotally supported by the pivotally supporting mechanism 73, and the other end of the rotary rod 72 is protruded, passing through a rod cover 74 of the cylinder main body 70. Further, a male screw 75 having a lead angle of 60 degrees or more is formed on an outer peripheral surface of a portion of the rotary rod 72 positioned within the cylinder main body 70.
A piston 76 fits over the rotary rod 72. The piston 76 thereby can slide within a cylinder tube 77, being in contact with the cylinder tube 77. A portion in which the piston 76 fits over the rotary rod 72 is constituted from a segment in which the piston 76 screws together with the male screw 75 of the rotary rod 72, a section in which the piston 76 fits over a round rod portion of the rotary rod 72, and a non-contact section interposed between the section where the piston 76 screws together with the rotary rod 72 and the section where the piston 76 fits over the round rod portion of the rotary rod 72. Inside the piston 76, a communicating hole 79 is formed. The communicating hole 79 communicates an inside of the non-contact section with a cylinder chamber 78 formed on a side of the section in which the piston 76 screws together with the male screw 75 of the rotary rod 72.
On the other hand, between the piston 76 and the cylinder main body 70, a rotation restraining mechanism that restrains relative rotation is formed. The rotation restraining mechanism is formed of a key 80 installed on an outer periphery of the piston 76 and a key groove 81 formed in an inner periphery surface of the cylinder tube 77 in FIG. 8.
When a port 83 that leads to a cylinder chamber 82 on a side of the rod cover 74 is connected to a drain and pressure oil is supplied through a port 84 that leads to the cylinder chamber 78 on a side of the head cover 71 in this configuration, the rotary rod 72 rotates in one direction with advancement of the piston 76, based on a screwing relationship between the male screw 75 of the rotary rod 72 and the piston 76 and the rotation restraining mechanism formed of the key 80 and the key groove 81. Conversely, when the port 84 is connected to the drain and the pressure oil is supplied through the port 83, the rotary rod 72 rotates in a direction opposite to the direction in which the rotary rod rotates with advancement of the piston 76, with retraction of the piston 76.
Round holes are formed in a product resulting from die casting or plastic injection molding using a core pin. Depending on the product, all or part of the round holes after molding must be sometimes formed into screw holes. In such a case, an additional process will be provided separately to process the round holes into the screw holes.
Accordingly, when a screw hole is included in a final product, the additional process must be incorporated, without exception. Further, since orientations of the screw holes for the product are not limited to one direction in general, automation of the process for obtaining the screw holes is often difficult. Thus, an increase in manufacturing cost may be inevitably brought about.
In order to cope with the problem described above, the following method can be conceived. As a core pin, a core having a required male screw (hereinafter referred to as a “screw core”) is used. Then, in the case of a diecast product, the screw core is inserted into molten metal, and when the molten metal is solidified, the screw core is retracted just by the number of pitches of the male screw for each rotation, for removal. Then, a resulting hole after the removal of the screw core can be formed into the shape of the required male screw.
The cylinder device (shown in FIG. 7) disclosed in Japanese Patent Unexamined Publication H10-131913 can cause the piston and rod 53 to retract while rotating the piston rod 53 by a large torque. Accordingly, it seems that the cylinder device can be employed for screw hole formation, in principle.
However, in this cylinder device, the piston and rod 53 is rotated, using the screwing relationship between the screw rod 55 and the screwing board 57. Thus, lead angles of respective screw portions of the screw rod 55 and the screwing board 57 are obliged to be set to be far larger than the lead angle of an ordinary screw. Accordingly, in terms of both a rotation pitch and a stroke length, the cylinder device shown in FIG. 7 cannot be applied as the cylinder device for removing the screw core.